441
FXUS63 KMQT 212352
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
752 PM EDT Mon Jul 21 2025

.KEY MESSAGES...

- Showers and thunderstorms are expected late Tuesday into early
  Wednesday. Stronger storms could produce heavy rain. There is
  a slight chance (15%) of exceeding flash flood guidance across
  far western Upper Michigan. Isolated severe storms are also
  possible (5%).

- Additional rounds of thunderstorms are possible Wednesday
  through Friday morning. Storms on Wednesday bring additional
  chances for strong to severe storms (15%) and heavy rain
  exceeding flash flood guidance.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 332 PM EDT Mon Jul 21 2025

A sfc high extending SW into the Great Lakes from N Ontario should
continue mostly dry weather through tonight as it shifts SE toward
the Lower Great Lakes. Some transient -shra can`t be ruled out over
the W this evening into tonight, currently lingering over NW WI this
afternoon after a MCS this morning tracked ESE over MN. This precip
will have to erode through a fairly dry resident air mass, but will
have some help from a mid level shortwave. QPF will be sparse and
low, if any, so no impacts are expected in the near term. Otherwise,
temps hold in the low to mid 70s outside areas where lake breezes
off both lakes have moderated temps down into the 60s. Lows by Tue
morning will be in the 50s to low 60s.

An active period then begins on Tue. Increasing S flow with the high
pressure shifting SE brings a warm and moist airmass in. This brings
temps into the mid 70s to mid 80s and Tds in the 60s, resulting in
MUCAPE increasing to 1000-1500j/kg over the W. Where uncertainty
still remains in the fcst is the timing of tsra. Tonight, two
shortwaves along the far W periphery of the Central/N Plains quickly
track NE toward the Great Lakes for late in the day Tue. This should
support convective activity within the unstable environment it
progress through. If this wave is on the progressive side and
arrives in the far W by 17/19Z on Tue like the 12Z HRRR/ARW/FV3,
instability may not be quite as high as a later arrival like the
NAMNest/RAP. Regardless, bulk shear should be sufficient for
organized convection ~30 kts or higher. Mid level lapse rates
approach 7C/km, low level lapse rates will struggle, and a few
hundred j/kg of DCAPE (likely 900j/kg or less) will be present late
in the afternoon/evening hours. This should be supportive for some
gusty winds and hail, especially within strong updrafts. With
PWATs/Specific Humidity increasing above the NAEFS 99th percentile
Tue night into Wed and a strong LLJ moving in over the W, heavy
downpours and resulting flooding risks are increased for later waves
and MCS development for Tue night into Wed. Otherwise temps only
settle into the 60s Tue night.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 415 PM EDT Mon Jul 21 2025

The active period continues through much of the work week as
multiple mid level shortwaves tracking E along fairly zonal flow
over the Great Lakes bring rounds of shra/tsra to the region. A
strong Gulf connection provides ample moisture primed for heavier
precip, noted well in the PWATs above the 99th climatological
percentile with values ~2-2.25" surging into the region for Wed.
With sufficient CAPE and bulk shear within the environment through
Thu, several rounds of tsra are likely with the incoming shortwaves.
This brings strong to severe potential with each round as well as a
marginal to slight flooding risk. The flooding risk is primarily
focused on Wed into Wed night when a warm front lifts overhead
followed by a slower moving cold front from the W. This is captured
well by WPC with a 15% chance of excessive rainfall over much of the
CWA outside the S-central and SE UP. A marginal risk (at least 5%)
is fcst otherwise through Thu. Primary threats accompanying the
heavy rain with the midweek wave include damaging winds and large
hail captured by the SPC Slight Severe Risk over most of our CWA.

A passing weak sfc high pressure brings a brief break from the
activity Fri/Sat, but low rain chances return Sat night/Sun as the
troughing returns. Otherwise, above normal temps dominate the fcst
with highs in the mid 70s to upper 80s and lows in the mid 50s to
60s.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 751 PM EDT Mon Jul 21 2025

VFR conditions and prevail at all TAF sites through the 00z TAF
period. Upstream in N WI and MN, a weak wave is kicking off some
light scattered -shra which may impact IWD tonight. Have included a
prob30 group through midnight to account for this scenario.
Elsewhere, mostly clear skies will give way to VFR cigs overnight.
Through this afternoon, some convective activity is expected in the
west-central UP, but given the stark differences in 00z CAM output,
holding on off timing until the 06z and 12z updates. Otherwise,
gusty S winds 15-20 kts will be on the increase after sunrise.

&&

.MARINE...
Issued at 332 PM EDT Mon Jul 21 2025

Light winds of generally 20 knots or less are expected to dominate
the rest of this week, although some southerly winds of 20 to 25
knots are possible over the eastern half of the lake Tuesday night
as the sfc low moves through Lake Superior. Some showers and
thunderstorms are expected across the lake this evening and once
again Tuesday through Thursday. Some the storms may be strong to
severe Tuesday through Thursday, bringing erratic/damaging winds and
large hail to the sfc.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.

&&

$$

SHORT TERM...Jablonski
LONG TERM...Jablonski
AVIATION...BW
MARINE...TAP